It's probably more ideal to have plants with the same nutrient requirements feeding from the same reservoir. Otherwise it is probably better to err on the side of under feeding rather than over feeding.

Feeding the larger plants with the seedling strength nutes is preferable to the risk of burning the seedlings with a stronger feed.

I grow a number of sacrificial mother plants in compost early in the season to supply enough sideshoots to populate the main systems in one go. Its easier to look after a few plants than dozens of seedlings. The sideshoots root in 4-6 days in a glass of water, 3-5 days in an aerocloner. The real benefit of using clones is they are genetically identical to the mother plant so take cuttings from mothers that show the best traits, such as health and vigor. With seeds, the traits are unknown until they grow :).